The invention relates to detection of unpressurized moving containers, particularly containers such as thin-walled aluminum cans.
Thin-walled aluminum cans, which are commonly used for storing beverages and other products, are typically filled and sealed on high speed canning lines. For quality control purposes, the cans must be inspected after filling and sealing to ensure that they have been properly sealed. Due to the operating speeds of many canning lines (e.g., 2400 cans per minute), this inspection must be extremely fast, and, for commercial reasons, the inspection must be extremely accurate.
One technique for detecting improperly sealed, or "unpressurized" cans in a stream of cans is to invert the cans and submerge them in a hot water bath. This causes air in each can to expand and to force the beverage or other products out of an improperly sealed can through any defect in the seal near the top of the can. The cans are then returned to their normal orientation, and the liquid level in each can is checked using, for example, radioactive isotopes or x-rays. If the liquid level in a can is below normal, this indicates that the can's seal is defective and the can is unpressurized, or that the can was underfilled, and that the can therefore must be rejected.